Most cannabis growers should hang LED fixtures 24 to 36 inches above seedlings, 18 to 30 inches above plants in veg, and 12 to 18 inches above plants in flower. HPS and CMH lamps run hotter and throw less usable light per watt, so they sit roughly 6 to 12 inches higher at every stage. Fluorescents and CFLs are the exception: they stay 2 to 12 inches from the canopy because their output is weak. Treat the chart below as a starting point, then confirm with a PAR meter or the back-of-hand test.

Cannabis Grow Lights: PPFD, DLI, and What to Buy

Cannabis grow light distance chart by lamp type and stage

LED (quantum board, bar, and COB fixtures, 100 to 1000W)

Modern LEDs deliver far more PAR per watt than legacy lamps, so the flowering end of this range only applies to fixtures run at full power. A 240W board in a small tent may sit closer than a 720W bar light in the same stage.

related article

HPS and CMH (hid lamps)

Air-cooled hoods and sealed reflectors let you hang a little lower because radiant heat is vented away. Without cooling, add 3 to 6 inches at each stage to protect the canopy.

more on this topic

Fluorescent and CFL

Weak output means weak light travels poorly, so these lamps are only useful for seedlings, clones, and mother plants. Keep them close or your plants stretch.

related article

Why distance matters less than PPFD and DLI

Distance is a proxy for intensity, and intensity is what actually drives growth. PPFD measures usable photons hitting the canopy each second, while DLI totals those photons across a 24-hour day. Common DLI targets are 15 to 25 mol/m2/day for seedlings, 25 to 40 for veg, and 40 to 60 for flowering with added CO2 pushing higher.

Two fixtures at the same height can deliver very different PPFD. That is why a chart alone can burn plants or leave them starved.

How do you tell if a grow light is too close?

Watch for bleached or yellow-white top buds, leaves curling upward like tacos, crispy tips, and stalled growth at the canopy while lower growth looks fine. Those are light stress symptoms, not nutrient problems. Run the hand test: hold the back of your hand at canopy height for 10 seconds, and if it feels uncomfortably hot, raise the light.

Should you dim or move the light instead of adjusting height?

Dimming is often the better move because it keeps coverage even across the whole canopy. Dropping a fixture too low concentrates light in the center and leaves corners dark. If your light has a dimmer, run it at 50 to 75 percent during veg and raise output in flower rather than slamming the fixture down.

Common grow light distance mistakes

FAQ

What is the best distance for a 1000W LED?

Roughly 36 to 48 inches in veg and 24 to 30 inches in flower, unless the fixture is dimmed. A 1000W LED at full power is too intense for most tents below 24 inches.

Does light distance change during flowering?

Yes. Flowering plants tolerate and need higher PPFD, so most growers lower the light or raise the output by 20 to 30 percent when switching to 12/12.

How far should a grow light be from seedlings?

Keep LEDs 24 to 36 inches away and HPS about 36 to 48 inches away. Seedlings have thin leaves and burn faster than mature plants.